ACEI, also called angiotensin-converting enzyme inhibitor, is a drug that inhibits the activity of angiotensin-converting enzyme. Angiotensin-converting enzyme, which catalyzes angiotensin I to produce angiotensin II, a strong vasoconstrictor, also stimulates the release of adrenal cortical aldosterone. The use of ACEI, first of all for the treatment of hypertension, after the drug makes the perigastric vasodilatation, the total peripheral resistance decreases, and the blood pressure falls, without reducing important cardiac, cerebral and renal blood flow or causing postural hypotension while lowering blood pressure. The use of ACEI drugs for the treatment of heart failure, by inhibiting and reducing the effects of angiotensin II and aldosterone in the body, allows the anterior and posterior loads on the heart to be reduced, resulting in a decrease in peripheral vascular coronary resistance, improving blood supply and contributing to the protection of the myocardium. The use of antihypertensive drugs with ACEI protects the kidneys by reducing the hyperperfusion of the kidneys and protecting the kidneys.